The present invention generally relates to mobile radiocommunication systems.
The present invention more particularly relates to CDMA (xe2x80x9cCode Division Multiple Accessxe2x80x9d) systems. In particular, the present invention is applicable to UMTS (xe2x80x9cUniversal Mobile Telecommunication Systemsxe2x80x9d).
CDMA is a multiple access technique which makes it possible for several users to share a common bandwidth by allocating different codes to these different users.
Code allocation enables the transmission at a given transmission rate, or else at a given transmit power, all representing a portion of a system capacity.
In such systems, there is a general need to make the most efficient use of available radio resources, by allocating these resources to users, according to needs, in the most efficient way.
One way to optimise the use of radio resources is to take advantage of periods of low activity in high priority traffic (such as for example silence periods in voice traffic), to transmit low priority traffic (such as for example packet data traffic).
Such an optimisation may especially be beneficial for downlink transmission, i.e. for transmission from a fixed station, also called base station, to mobile stations, or users, served by this fixed station. In this way, a residual transmit power may be allocated for low priority traffic, as for as the sum of this residual transmit power and of the transmit power used for high priority traffic, at each instant, does not exceed the total transmit power available at the base station. This is disclosed for example in WO 98/35514.
A problem is how to share such a residual capacity between such low priority users. In the cited reference, this residual capacity is shared between such users (called scheduled users) on a priority basis. At each frame, a scheduled user having the highest priority is allocated a portion of the residual capacity, taking into account the capacity requirements for this user, then the residual capacity is updated to take into account the just allocated capacity. This is repeated for a next scheduled user of lower priority, and so on, each scheduled user thus getting a portion of said residual capacity then being allocated the corresponding required codes.
With such a solution, scheduled users having lower priorities may have to wait quite a long time before being served, depending on the number of more prioritary scheduled users, and on the amount of data to be transmitted to such more prioritary scheduled users.
The present invention is based on a different approach for sharing such a capacity between such users, enabling in particular to guarantee given number of users to be served at each instant. The present invention is not limited to the case where the thus shared capacity is a residual capacity as recalled above; the present invention may be applied to any case where it may be useful to share capacity in such a system, between a given number of users of this system.
An object of the present invention is therefore a method for sharing capacity in a code division multiple access mobile radiocommunication system, between a given number of users of said system, a method wherein said given number is predetermined, said method including a step of allocating code resources to said users, as a function of said predetermined number.
According to another object of this invention, said capacity corresponds to a residual downlink capacity, not used at a given instant for high priority traffic, and said users sharing said residual capacity correspond to low priority traffic users.
According to another object of this invention, said step of allocation of code resources to said users includes a first step, whereby code resources are allocated so that said capacity is evenly shared between said users.
According to another object of this invention, said step of allocation of code resources to said users includes a second step, whereby code resources thus allocated in said first step are adapted, so as to take into account the capacity requirements for each user.
According to another object of this invention, said second step includes
a step of controlling if the sum of the capacities which would be allocated to said users, using the code resources thus allocated in said first step, and taking into account the different capacity requirements for each of said users, does not exceed said capacity,
a step of adapting the code resources allocated to at least one of said users, if said sum exceeds said capacity, said adaptation being carried out in a way that said sum no longer exceeds said capacity.
According to another object of this invention, said allocation of code resources includes allocating to each of said users a code length required for sharing said capacity between said users.
According to another object of this invention, said first step includes allocating a some code length to each of said users.
According to another object of this invention, said method further includes a step of determining said given number of users.
According to another object of this invention, said given number of users is determined as a function of said capacity and of users"" needs.
According to another object of this invention, said method further includes a step of dividing said users into different groups having respective priorities, and sharing said capacity between said different groups, according to said respective priorities.
According to another object of this invention, sharing said capacity between said different groups is carried out in the time domain.
According to another object of this invention, said sharing in the time domain is performed on a data unit period, or frame, basis.
According to another object of this invention, said steps are performed dynamically.
According to another object of this invention, said steps are performed on a data unit period, or frame, basis.
The present invention also has for its object a mobile radiocommunication network entity (such as base station and/or base station controller) for performing such a method.